How to embed flash and/or EEPROM in MCU ASIC

[xuanjie]

I am having some question related to embedding flash and/or EEPROM in my MCU ASIC design.
(1) Isn't it true that flash requires a different process technology than CMOS? If that's the case, how can I put flash and the control logic into a single die?
(2) Is it true that I can get some kind of flash IP from some companies, or even the foundry themselves?
(3) Is there any ebook or paper to discuss thie topic?

Any reply would be welcomes, thanks for your time.

 

[computer_terminator]

1. Yes, you need to use flash process to make your ASIC instead of std. CMOS process.

2. You will get flash IP or flash compiler from the IP provider or foundry.

3. It will be better to contact ASIC vender or foundry. They will give you more information.

 

[vsop]

(3) basically, the main issue of embedding flash/eeprom in asic is on the programming circuits and the protection circuits. programming ckt. provides the path from the programmer external to the asic to the internal flash/eeprom. the most straight way is the dedicated ckt., but the programmer will be a problem. the most easy way is the common rs-232 serial path, and the programmer is pretty easy to inplement. the most "advanced" way is jtag, and the programmer is not so difficult to find. the protection ckt. means that used to avoid the damage of the contents of flash/eeprom during the un-stable period, such as power-on/off. thus the recommandation to the embedding flash/eeprom design is keeping some code space as rom instead of whole flash/eeprom. putting some boot-loader in this space will be much safer in all of the cases. besides, isp/iap methods will also affect the implementation.

 

[xuanjie]

books or websites for this?

Thanks a lot for your advice. Is there any books or websites that offer good information on this area?

 

[electronrancher]

i think flash process is not compatible with standard cmos - many cmos processes cannot make the thin tunnel oxide and the normal mosfet oxide. also the flash floating gate is not really easy to fabricate with standard poly gate processes.

that's not to say that a guy with a good cmos process can't make flash, but it uses some special processing that most of the MOSIS guys don't do.

also, since programming voltage is about 12-14v, this is above the breakdown voltage of many small cmos processes (around 4-8v). you need HV mosfets as well as the tunnel oxides and floating gates. THEN you can make flash.

TSMC sells a block of flash to drop into your asic design, I think around $30K to license this. The flash is very good quality and easy to use - originated by SST (silicon storage). I think it uses a split-floating gate. Only if floating gate is charged (programmed) and normal gate is on does the cell flow current. Very reliable, but individual will have a hard time to pay this licensing fee. But hey, a single process run of 24 wafers is around $65k from them (If I remember correctly), so maybe if you have good funding this does not sound like a lot of money.. to me, it's WAY too much! I mgiht use external program memory, and build my micro on a cheap 0.5um process.